The present invention relates to the construction of a field effect transistor oscillator frequency controlled by a d.c. voltage. The invention applies to all types of oscillators based on a field effect transistor, but is more particularly advantageous in the ultra-high frequency range, e.g. in the X band, in which are used GaAs transistors or more generally transistors made from materials of types III-V. At these frequencies, the length of the connections between the oscillator components contribute to a significant modification of the frequency. The structure adopted for the oscillator according to the invention makes it possible to stabilize the oscillator output power with a good frequency linearity in an approximately 1 GHz band, which constitutes a narrow band, but which is still broader than that of e.g. diode oscillators.
In the present state of the art, oscillators operating in the X band, i.e. 5.2 to 11 GHz are constructed in hybrid circuit form, i.e. by the connection on a substrate or in a box or case of discrete components, which are interconnected by metallizations on the substrate or by metal wires in air. At these frequencies, the length of the wires is by no means unimportant and as a result of the reactance thereof can modify the frequency of the oscillator.
Moreover, the known oscillators are often based on a Gunn effect diode and a varactor, i.e. a voltage-controlled, high power variable capacitor. They suffer from the disadvantage of a poor ultra-high frequency efficiency of only roughly 3% and are only linear in frequency as a function of the control voltage in a very narrow band of approximately 300 MHz. The lack of output linearity makes it necessary, if a broad band is required, to use several oscillators in parallel and/or discriminators which lead to supplementary insertion losses in an apparatus not having a high efficiency.